1. Technical Field
The present invention relates to a pivot assembly bearing used in a hard disk drive, and in particular, relates to an adhesive used in the pivot assembly bearing.
2. Background Art
A hard disk drive is one type of storage device used in computers. As shown in FIGS. 1 and 2, a hard disk drive D writes information to a magnetic disk 5 and reads the written information from the magnetic disk 5, by moving over the magnetic disk 5 a magnetic head 4 arranged at the tip of an actuator 3 swingably supported by a pivot assembly bearing 1. The pivot assembly bearing 1 ordinarily has a structure in which two ball bearings are arranged between a shaft and a housing (sleeve) surrounding the shaft, and they are supported by an upper supporting part 2 and a lower supporting part (not shown).
Recently, accompanied by higher information capacity and speeding up of reading and writing, in order to correctly read and write the information recorded on a magnetic disk, it has become more important to maintain cleanliness in the hard disk drive. Therefore, a need to reduce so-called “outgas” originated from the vaporization of adhesive used in the hard disk drive, which affects the constitutional parts of the hard disk drive, has become more stringent. At the same time, a need to reduce the cost of pivot assembly bearings is also becoming more stringent.
To meet such needs, a well-known technique is to use a UV curable type anaerobic adhesive in a pivot assembly bearing for fixing a ball bearing inner ring to a shaft and a ball bearing outer ring to a housing. For example, a pivot assembly bearing which is fixed by using UV curable anaerobic adhesive having a monomer composition consisting of 80 to 96 mol % of methacrylic diester, 2 to 10 mol % of hydroxyalkylmethacrylate, and 1 to 10 mol % of acrylic acid dimer; 1 to 5 parts by weight of photopolymerizing agent per 100 parts by weight of the monomer composition; and 0.2 to 2 parts by weight of organic hydroperoxide per 100 parts by weight of the monomer composition, is disclosed (see Patent Document 1).
Patent document 1: Japanese Patent No. 3995490
However, even the pivot assembly bearing disclosed in Patent Document 1 is not sufficient to satisfy the requirement for reducing outgas and cost, which have become more stringent recently.